Stock Options and Incentive Plans (Schedules of Executive Management Share-based Compensation Activity) (Details) - Performance Shares [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Number of shares
Shares/Share units potentially payable, beginning balance	188,308	185,199	185,564
Forfeitures
Payments	(86,926)	(95,889)	(75,385)
Shares accrued	88,036	98,998	75,020
Shares/Share units potentially payable, ending balance	189,418	188,308	185,199
Weighted average grant date value per share
Shares/Share units potentially payable, beginning balance	$ 35.35	$ 30.69	$ 27.51
Forfeitures
Payments	33.43	29.09	28.60
Shares accrued	36.78	38.01	34.65
Shares/Share units potentially payable, ending balance	$ 36.90	$ 35.35	$ 30.69
Year-end intrinsic value
Shares potentially payable	$ 6,657	$ 5,683	$ 6,667
Shares potentially payable	$ 6,989	$ 6,657	$ 5,683